This invention relates to a method of annularly applying a rubber layer, so-called bead apex or bead filler, which is formed by extrusion to have a relatively slender and substantially triangular cross-section, to the peripheral surface of a bead ring for an automobile tire prior to the application of the bead ring with a bead apex to the tire building former in tire manufacture and a device for realizing this method.
Principal prior art techniques of this kind are disclosed, for example, in Japanese patent publication gazette Nos. 51-29551 and 61-6782. It is described, in the former, that the leading end of an apex is fed onto a rotating bead ring suspended between a pair of guide rollers and continously pressed against the peripheral surface of the bead ring by a pair of press rollers to be applied annularly thereto, that the bead apex is pinched between a disc roller and a cone roller so as to forcibly stretch it from the inner edge to the outer edge during the apex applying process, that arrival of the leading end of the apex at a predetermined position is detected and the bead apex is cut in a predetermined length at the tail end thereof, that both cut ends of the apex which are left open in V-shape are clamped and drawn into contact by a splicing mechanism to bond both cut ends together after the apex is applied to the whole peripheral surface of the bead ring, and so on.
It is described, in the latter, that a bead ring is held on the periphery of a rotatable disc and a bead apex previously cut in a predetermined length is annularly applied to the peripheral surface of the bead ring with rotation of the disc, and that, when both ends of the bead apex face to form a V-shaped gap therebetween, both ends are caught from respective side surfaces by two pairs of catching members (pressing elements) and a thrust force is applied to the catching members by a third mechanism, thereby drawing near both the V-shaped facing ends until they butt against each other to be bonded together.
When a bead apex having a relatively slender triangular cross-section is applied annularly to a bead ring, a V-shaped gap is unavoidably formed between the leading and tail ends of the apex due to the difference between the inner and outer circumferential lengths of the annular bead apex lying on the peripheral surface of the bead ring. According to the above-mentioned prior art techniques, both ends of the bead apex are caught by pincers-type catching members and mutually drawn near to make a butt joint after the bead apex is applied to the peripheral surface of the bead ring. However, this has given rise to such problems in that the bead apex contracts especially in its outer edge region in the period from the drawing out of the bead apex to the completion of the application of the bead apex to the bead ring and, therefore, the V-shaped gap expands more by the amount corresponding to this contraction, that the apex is locally deformed in the vicinity of the joint in order to remove the V-shaped gap and this local deformation results in a corresponding local irregularity of the peripheral shape of the bead apex, and that undesirable catching marks of the catching members may remain in and near the joint. The size of the V-shaped gap is not always fixed and it is sometimes large and some times small, since the degree of contraction of the bead apex rubber varies with its viscosity. The above-mentioned pincers-type catching members of the prior art cannot effect a free drawing motion conformable to the size of the V-shaped gap but a limited motion only. More particularly, if the operation stroke is set large for avoiding misjoint, an over-joint (excessive bond) may be resulted from bonding or a small gap. Inversely, if the operation stroke is set small in accordance with a small gap, an insufficient joint including residual openings may be resulted from bonding of a large gap.